The present invention relates to truck tires, preferably super single radial truck pneumatic drive tires.
Super single tires, which are wide base low aspect ratio truck tires replacing two small base tires, so-called dual mounted tires, have been used for years on trailers. Such tires are usually of size 385/65R22,5 or 385/55R22,5 and have a maximum load-carrying capacity of 4,5 metric tons.
Over the years these wide base tires appeared more and more on trucks in the steering position because they had a higher mileage.
Recently it became of interest to use also super single tires in the drive positions. Tires in the drive position have to bear part of the trailer load and must have an increased load capacity. Tire standards define a load capacity of 5,8 metric tons and a maximum speed of 110 km/h. These tires have very low aspect ratios and are usually of size 495/45R22.5. Drive tires are exposed to harsh service conditions and conventional constructions show crown area durability problems. Furthermore the pressure distribution through the elastomeric blocks in the footprint lacks the required uniformity.
GB-A- 1 567 614 discloses a pneumatic tire particularly suitable for heavy vehicles. Radially outwards of the breaker layers there is at least one layer comprising metallic cords parallel to one another and substantially parallel to the circumferential direction. The metallic cords have an ultimate elongation between 4 and 8%. In a preferred embodiment the layers of extensible metallic cord are formed by a single helically wound cord.
It is known from LU-A- 85 964 to wind a ribbon reinforced with cords helically in at least two layers on top the belt plies of a passenger tire. The ribbon has a width comprised between 15 and 45 mm. The reinforcing cords are preferably of nylon and have a lateral density of about 30 EPI.
FR-A- 2 285 255 discloses a crown reinforcing structure for pneumatic tires including a helically wound ribbon reinforced with steel cords. The ribbon has a width comprised between 5 and 50 mm and is directly wound on the carcass ply.
It is an object of the present invention to provide a super single radial truck tire having a crown reinforcement giving improved crown area durability
A further object of the present invention is to provide a super single radial truck tire having a crown reinforcement resulting in an improved footprint shape and footprint pressure distribution.
Yet another object of the present invention is to provide a super single radial truck tire having excellent high speed properties and improved wear properties.
Still, another aspect of the present invention is to provide a radial super single radial truck tire optimizing the trade-off between handling and durability.
A pneumatic medium truck tire of the invention comprises at least one pair of parallel annular beads, at least one carcass ply wrapped around said beads, three to six belt plies disposed over the at least one carcass ply in a crown area of the tire, a tread disposed over the belts, and sidewalls disposed between the tread and the beads. At least one of the radially inner belt plies is obtained by helically winding an elastomeric ribbon reinforced with high elongation steel cords.
In various embodiments of the invention, the helically wound belt plies are reinforced with high elongation steel cords having the construction 3xc3x977xc3x970.22.
Specific constructions of such tires are also claimed.